Manganese acetate, reaction with aldehydes

Routes via o-aminophenylpyrroles present the most convenient syntheses of a wide variety of pyrrolo[l,2-a]quinoxalines. Thus reaction of the amino compound 6 with acetic anhydride in acetic acid gave the acetamido derivative which was cyclized with phosphoryl chloride to give the 4-methyl compound 7 (R = Me) in 56% yield. The 4-phenyl compound 7 (R = Ph) has been prepared similarly. An even more convenient synthesis of 4-aryl compounds is achieved by reaction of compound 6 with aromatic aldehydes to give the 4,5-dihydro derivatives These are readily oxidized to 4-arylpyrrolo[l,2-a]quinoxalines 9 with manganese dioxide. This approach may be carried out in one step by reaction of compound 6 with aromatic aldehydes (e.g., benzaldehyde) in the presence of cupric acetate. Reaction of the aminophenylpyrrole 6 with 90% formic acid gave pyrrolo[l,2-a]quinoxaline (7, R = H) directly in 98% yield. Pyrrolo[l,2-a]quinoxalines substituted in the l-position and the 7-position have also been prepared from appropriately substituted... 

A route to canthaxanthin using Wittig reaction methodology has been described (ref. 50). In this approach retinol (vitamin A) was oxidised in dichloromethane with manganese dioxide to retinal (vitamin A aldehyde) which was converted to 4-acetoxyretinal by bromination with N-bromosuccinimide in dichloromethane containing acetic acid. By reaction with retinyltriphenylphosphonium hydrogensulphate derived by reaction of triphenylphosphine with retinol hydrogensulphate, isocryptoxanthin acetate was obtained. Treatment of this with 68% hydrobromic acid formed... 

Pinacol coupling and attylation. Either activated manganese alone" or Mn-CrClj-MejSiCl effects pinacol coupling of aromatic aldehydes. The reaction can also be mediated by Mn in aqueous acetic acid, but with Mn-Cu and in the presence of allyl halides allylation becomes the major reaction course. ... 

Manganese(III) can oxidize carbonyl compounds and nitroalkanes to carboxy-methyl and nitromethyl radicals [186]. With Mn(III) as mediator, a tandem reaction consisting of an intermolecular radical addition followed by an intramolecular electrophilic aromatic substitution can be accomplished [186, 187). Further Mn(III)-mediated anodic additions of 1,3-dicarbonyl and l-keto-3-nitroalkyl compounds to alkenes and alkynes are reported in [110, 111, 188). Sorbic acid precursors have been obtained in larger scale and high current efficiency by a Mn(III)-mediated oxidation of acetic acid acetic anhydride in the presence of butadiene [189]. Also the nitromethylation of benzene can be performed in 78% yield with Mn(III) as electrocatalyst [190]. A N03 radical, generated by oxidation of a nitrate anion, can induce the 1,4-addition of aldehydes to activated olefins. NOj abstracts a hydrogen from the aldehyde to form an acyl radical, which undergoes addition to the olefin to afford a 1,4-diketone in 34-58% yield [191]. 

Acetaldehyde—Acetic aldehyde—Acetyl hydrid——44 —is formed in all reactions in which alcohol is deprived of H without introduction of O. It is prepared by distilling from a capacious retort, connected with a well-cooled condenser, a mixture of HjSOj, 6 pts. HgO, 4 pts. alcohol, 4 pts. and pow dered manganese dioxid, G pts. The product is redistilled from calcium ehlorid below 50° (123° P.). The second distillate is mixed with two volumes of ether, cooled by a freezing mixture, and saturated with dry NHg there separate crystals of ammonium acetylid, CgHiO, NHi, -which are -washed with ether, dried, and decomposed in a distilling apparatus, over the water-bath, with tho proper quantity of dilute HjS04 the distillate is finally dried over calcium ehlorid and rectified below 35° (95° P.). 

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